1. Field of the Invention
The present invention relates to a semiconductor device and a method of fabricating the same. More particularly, the present invention relates to a semiconductor device having a metal gate and a method of fabricating the same.
2. Description of Related Art
With the continual miniaturization of semiconductor devices, sizes of gate structures are also gradually reduced. Therefore, the thickness of gate dielectric layers also needs to be reduced to prevent the performance of the devices from being affected. Generally, the material of the gate dielectric layers usually includes silicon oxide. However, the leakage current phenomenon frequently occurs when reducing the thickness of the gate dielectric layers adopting silicon oxide.
In order to reduce the occurrence of leakage current, the conventional method is to replace silicon oxide with high dielectric constant (high k) material for the gate dielectric layers. When applying high dielectric constant material as the gate dielectric layers, the gates adopting polysilicon then react with high dielectric constant material to generate Fermi-level pinning, thereby resulting in an increase in the threshold voltage so as to affect the performance of the device.
In one of the conventional techniques, the metal layer is applied as the gate, that is, the work function metal layer known in the art, to prevent the threshold voltage from increasing and therefore reducing the resistance of the device.
However, conventional semiconductor devices have a difficulty in lowering the band-edge work function, and therefore the semiconductor devices with superior electrical characteristics can not be provided.